IACS Unified Requirements + Interpretations
The International Association of Classification Societies (IACS) publishes two categories of shared technical standards adopted by all 12 member societies (ABS, BV, ClassNK, CCS, CRS, DNV, IRS, KR, LR, PRS, RINA, RS): Unified Requirements (UR) and Unified Interpretations (UI). URs set out the minimum technical requirements that member societies must apply through their rules; UIs provide clarification of statutory-instrument text (SOLAS, MARPOL, STCW). Together they constitute the core class-society common technical baseline — the reason a vessel classed by any IACS member is considered equivalent by any other member.
UR series structure
- UR S (Strength / Structural). Hull structural requirements — plate thickness, welding, corrosion allowance, common-structural-rules (CSR) for bulk carriers + tankers.
- UR M (Machinery). Machinery requirements — main engine, boilers, auxiliary, shafting, propellers.
- UR W (Welding). Welding procedures, consumables, non-destructive examination.
- UR E (Electrical / Cyber). Electrical installations + protection + increasingly cyber requirements.
- UR Z (Survey). Class survey scope + frequency + reporting.
- UR I / L / P. Other specialised areas — piping, life-saving-appliances-related.
Notable current UR requirements
| UR | Topic | Application |
|---|---|---|
| UR S27 | Fatigue strength — cyclic-loading assessment for hull structural details | Post-2020 newbuild |
| UR S31 | Fatigue design assessment — common structural rules (CSR) | Bulk carriers + tankers CSR |
| UR M78 | Fuel-oil handling systems + safety design | All |
| UR E26 (mandatory 1 Jul 2024) | Cyber resilience of ships — new-build cyber-secure-by-design requirements | New builds contracted from 1 Jul 2024 onward |
| UR E27 (mandatory 1 Jul 2024) | Cyber resilience of on-board systems + equipment (OT layer) | New builds contracted from 1 Jul 2024 onward |
| UR Z10 series | Enhanced survey program (ESP) for bulk carriers + tankers | Ships over 500 GT |
| UR Z13 | Bulk-carrier survey + inspection | Bulk carriers |
| UR S11A | Longitudinal strength standard — all ship types | Structural design |
| UR S12 | Common structural rules for bulk carriers + oil tankers | CSR bulk + tanker |
| UR S17 | Longitudinal strength of hull girder in flooded conditions | Damage stability |
| UR S18 | Bulk-carrier fatigue strength for post-Erika/Prestige era single-hull-to-double-hull conversions | Structural fatigue |
| UR M74 | Redundancy requirements for machinery — DP-class-support | DP class |
| UR M75 | Emergency generator + emergency source requirements | Emergency machinery |
| UR M87 | Fuel-oil handling for LNG-dual-fuel + methanol-dual-fuel engines | Alternative fuels |
| UR I2 (Ice) | Polar Class hull-strengthening requirements | Polar Class |
| UR I3 (Ice) | Polar Class machinery requirements + winterisation | Polar Code |
| UR L1-L11 (Life-Saving) | Life-saving appliances series covering lifeboats + fast rescue boats + immersion suits + davits + release mechanisms | SOLAS III |
The UR E26/E27 cyber breakthrough (2024)
UR E26 (Cyber Resilience of Ships) and UR E27 (Cyber Resilience of On-Board Systems + Equipment) are the most significant recent addition to IACS URs. Effective for new-build vessels contracted on or after 1 July 2024, they impose cyber-security-by-design requirements at the shipyard newbuild stage:
- Network segmentation between IT (business) + OT (operational technology) systems.
- Access control + authentication for administrator-level access.
- Software patch-management processes documented in the SMS.
- Incident response + recovery procedures.
- Cyber-security training for crew — a significant STCW-adjacent obligation.
The requirements interlock with IMO Res. MSC.428(98) (2017) on the Maritime Cyber Risk Management framework + MSC.1/Circ.1420 (2012) cyber guidelines. See /reference/cyber-securityfor the broader framework.
IACS Unified Interpretations (UIs)
UIs clarify SOLAS, MARPOL, STCW, and Load Line Convention text. Where the Convention wording is ambiguous or has been subject to divergent interpretation, IACS members agree a common interpretation to prevent divergence in class certification. UIs are numbered UI-SOLAS-XX (SOLAS-related), UI-MARPOL-XX, UI-LL-XX (Load Line), UI-STCW-XX. Approximately 180 UIs are currently in force.
See also
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